While the invention can be used for joining and separating a variety of forms of sheets material including fabrics, wall surfacing materials and the like, the invention will be described hereinafter in relation to the joining and separating of carpet material.
It is well known to join adjacent abutting edges of carpets with a joining tape which is adhered to the carpet backing by an adhesive which may be either a solvent adhesive or, more recently, a heat softenable adhesive. In one known system, a carpet bonding tape is used which consists of a layer of material, such as paper, a layer of fabrice, woven material or other reinforcing material and an upper layer of a heat softenable adhesive composition, the nature and thickness of the heat softenable adhesive composition being such that an adhesive bond is formed between the fabric, woven material or reinforcing material and the underside of a carpet material when the tape is used in an operation in which heat is applied to the carpet and the adhesive by a heated "iron" which is moved along the seam to be joined. When the carpet material is pressed onto the heat softened adhesive layer and the heating source removed, the adhesive sets to thereby bond the carpet edges to the fabric, woven material or other reinforcing material.
The application of heat by the method described above to "melt" the adhesive is extremely difficult to control and a danger exists of burning or melting the carpet pile and/or backing.
Australian Pat. No. 464,878 describes a carpet bonding tape which consists of a layer of heat insulating material such as paper, a layer of metal foil and an upper layer of a ribbon of heat softenable adhesive composition, the nature and thickness of the ribbon of heat softenable adhesive composition being such that an adhesive bond is formed with the underside of a carpet material when the tape is used in an operation in which the carpet material is pressed onto the heat softened adhesive layer. The adhesive composition is softened by passing an electric current through the metal foil. A woven textile material may also be embedded in the ribbon of adhesive material to reinforce the tape.
In my U.S. application Ser. No. 171,865 filed July 24, 1980, I have described an improved method and apparatus for joining sheet material wherein the electrical current flow through the metal foil is controlled to thereby control the degree of softening of the adhesive to enable the carpet join to be correctly aligned prior to being adhered to the bonding tape.
While the carpet joining methods previously described generally provide a relatively firm joint between the edges of adjacent sheets of carpet material, it has been found that the cost of the electrically heated carpet bonding tape including the integral metal foil strip is relatively high. It has been thought necessary to bond the metal foil strip to the other layers constituting the carpet bonding tape i.e. the paper backing, reinforcing and adhesive materials, in order to ensure even heating of the adhesive and accurate alignment of the tape beneath the edge portions of the carpet material to be joined. However, I have now found that it is not necessary to fix the metal foil layer to the layers of other materials in the carpet bonding tape and that better and more economical results can be achieved with the tape and method of my invention.
Further, after carpet has been laid for some time a certain amount of stretching occurs which requires the carpet to be relaid if optimum appearance and wearing qualities are to be maintained. Such relaying generally requires separating and rejoining abutting edges to maintain correct alignment thereof. Carpet edge portions which have been joined with a tape using a heated iron to melt a heat softenable adhesive are extremely difficult to separate and to remove the joining tape therefrom.
Still further, in carrying out methods of joining carpet edges using an electrically heated carpet joining tape the electric current required to pass through the foil to soften the adhesive varies with ambient temperature and also varies as the temperature of the foil increases. Such variations may result in an initial current flow through the foil which overloads the electrical supply circuit to which the controlling apparatus is connected.
It is therefore an object of the present invention to provide an improved method for joining sheet material in edge-butting relation whereby the join may be relatively quickly, simply and economically made.
It is a further object of the invention to provide a method for separating carpet joining tape which has been previously bonded to carpet edge portions with a heat softenable adhesive.
A still further object of the present invention is to provide a tape which may be used in the joining of carpet edge portions and in separating a joining tape from such edge portions.
A still further object of the invention is to provide apparatus which may be used in conjunction with a carpet bonding tape utilizing an electrically heated metal foil whereby the current flow through the foil is maintained substantially constant during heating thereof.